Iron-air batteries are not for applications that require energy/mass density, like laptops and electric vehicles. They’re for fixed infrastructure like grid-scale batteries, where energy/$ is the relevant function. It needs to be almost literally as cheap as dirt.
They seem very focused on grid applications, yes. Beyond their key claim of a 10x cost advantage over lithium, it seems like they're only claiming the batteries will hold a charge for around a hundred hours: not at all good for long-term storage or devices, but perfectly reasonable for the grid.
Meaning background discharge is quite high, impacting efficiency. Good enough to smooth daily peaks though
Also, 10x cheaper than pricy
li-ion might not be enough, there are lots of other [weird] solutions, like pumping water up. Better question - how many cycles will battery last? This impacts price a lot
Shuttling water around, though, depends on having a bucket big enough and high enough to put enough water into to matter. A big ol’ bucket of rust might be easier to site if you don’t have a dam or a hillside reservoir handy.
I think this was just poor wording in the article. My local power company (Dominion Energy VA) recently started a huge iron-air battery project because the technology supports 100 hours of active discharge [0]. I'm sure there's some background discharge, but it takes a lot longer than 100 hours for iron to naturally rust through.
Is there any kind of grid-scale seasonal storage technology on the horizon? Batteries seem right out from the gate unless the cost drops to 1/10 of current. The only practical one I see is synthesizing a fuel (methane, hydrogen, whatever) which can be stored ~forever.
This isn’t exactly what you are asking for, but in terms of seasonal storage, the ground is at least commonly used in district heating and cooling systems via borefields as essentially a thermal battery. Buildings reject heating into the loop during summer, and it then gets dumped into the ground at the bore field, and similarly, in winter the pull heat from the loop which comes from the bore field. Ultimately, this relies on the fact that the borefield is already essentially at the right temperature to start (which is pretty trivial to achieve at a depth of around say 200m). One caveat is that if you live in a heating-dominated climate (so cold and snowy), you need to inject heat into the ground so that that the net balance of the thermal demand on the year is unbiased. However, you could see a version of this where you actually just overcool your buildings in summertime when you have excess solar potential, and then pull that heat back out in winter and end up balanced. This strategy wouldn’t work in a cooling-dominated climate unless you have excess clean electricity in winter but not summer.
From the perspective of the grid, this would effectively be a form of seasonal storage, since you no longer need to spend any electricity to inject heat into your borefield for balancing purposes, and additionally, you would have lower DeltaTs in winter than you would otherwise so your heat exchanger efficiencies ought to improve.
Edit: It’s almost certainly a better idea to use proper batteries that operate on the timescale of a day to soak up the excess electricity during the day and reuse it during the evening peak, rather than use the excess to pump heat into the ground, but still, there might be at least something there if there is a need for truly seasonal storage…
Maybe I will try to run some sims of this kind of system sometime over the summer.
Assuming you can just store it as piles of iron dust (somehow shielded from air/oxygen) and assuming a gross density of 5 t/m³ for iron dust you'd get a volumetric energy density in the ballpark of 10,000 kWh/m³.
